In the manufacture of a device such as a semiconductor device or the like, a process of filling silicon into a trench formed on an insulating film is performed. The silicon filled into the trench can be used as, e.g., an electrode.
In a process of the related art, a polycrystalline silicon film is formed on a wall surface of a workpiece, that define the trench. Subsequently, an amorphous silicon film is formed on the polycrystalline silicon film. Thereafter, the workpiece is annealed. In this process, by annealing the workpiece, amorphous silicon is moved toward the bottom portions of the trench, whereby the trenches are filled with the amorphous silicon.
However, the polycrystalline silicon film has a problem in that the flatness of the surface thereof is low. Since the growth of the polycrystalline silicon film is performed at a relatively high temperature, the polycrystalline silicon film has a large stress due to the thermal hysteresis. For that reason, a stress difference in an interface between the polycrystalline silicon film and the amorphous silicon film grows larger. The amorphous silicon becomes less fluid during the annealing due to the stress difference and the low flatness. As a result, cavities called voids or seams are formed in the silicon film that fills the trenches.